Audio problem: When the droid army are marching into battle at the end we hear a marching army, but they're walking on grass and the sound should be muffled in some way.
Audio problem: After the transport is destroyed in the hangar (near the beginning of the film) the scene cuts to Obi-Wan and Qui-Gon. The sound of their lightsabers being activated occurs before they even draw them from their belts.
Continuity mistake: When Obi-Wan is hanging from the ledge in the abyss after Darth Maul knocks him into it, he sees Qui-Gon's lightsaber a distance from him and uses the force to grab it. Between shots, the lightsaber changes position on the floor.
Chosen answer: According to "Inside the Worlds of Star Wars: Episode I" by Kristin Lund, they are "laser doors which lock into position in response to potentially lethal power outputs that occur intermittently during plasma activation process" (the fight takes place in a plasma energy processing plant). There are six laser doors in deference to an ancient Naboo legend in which Chaos is held back by six inpentrable gates. As you say though, they're really just a plot device to add dramatic tension to the duel!
Sierra1 ★